Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $96.97   4.250%   $101.0912   $101.09   $101.10   $101.10  
  Purchase #2 $151.42   10.160%   $166.8043   $166.80   $166.80   $166.80  
  Purchase #3 $67.39   12.527%   $75.8319   $75.83   $75.85   $75.80  
  Purchase #4 $106.54   3.307%   $110.0633   $110.06   $110.05   $110.10  
  Purchase #5 $229.97   4.788%   $240.981   $240.98   $241.00   $241.00  
  Purchase #6 $244.50   12.787%   $275.7642   $275.76   $275.75   $275.80  
  Purchase #7 $229.81   13.812%   $261.5514   $261.55   $261.55   $261.60  
  7 purchase totals = $1,126.60       $1,232.0873   $1,232.07   $1,232.10   $1,232.20